Impact mill



March 16, 1965 c. w. HUNT 3,173,620

IMPACT MILL Filed April 27, 1962 5 Sheets-Sheet 1 l'nveniow Cha /es Warr n fi/a z 5 Sheets-Sheet 2 c. w. HUNT IMPACT MILL March 16, 1965 Filed April 27, 1962 chair e5 warren F S lw Y a a M v o L March 16, 1965 c. w. HUNT 3,173,620

IMPACT MILL Filed April 27, 1962 5 Sheets-Sheet 3 March 16, 1965 c. w. HUNT 3,173,620

IMPACT MILL Filed April 27, 1962 5 Sheets-Sheet 4 Irv 8n ow Char/e Mag/ Ham By ihvgWMM f/f ion n eys C. W. HUNT IMPACT MILL March 16, 1965 5 Sheets-Sheet 5 Filed April 27, 1962 Inven-l'or Cha les Warren Hqn AHowneys United States Patent 3,173,620 IMPACT MILL Charles Warren Hunt, Calgary, Alberta, Canada, assignor to Industrial Coal and Minerals Ltd, Calgary, Alberta, Canada, a corporation of Canada Filed Apr. 27, 1962, Ser. No. 190,635 Claims priorit application Canada, Nov. 14, 1961, 835,997 9 Claims. (Cl. 241284) This invention relates to an impact mill and more particularly to an impact mill for attrition reduction in size of rock particles by the impact or collision fracturing of the particles to obtain a smaller substantially rounded product.

The applicant is not aware of any commercial apparatus or method for producing a substantially rounded product of the nature of sand from particles of rock. Several known commercial apparatus and methods deal with impact pulverization in which coarsely ground raw material is circulated at high velocity in an elastic fluid in a chamber having a closed continuous circuit. The moving particles of material collide with each other and as a result of these mutual impacts the material is pulverized. Other forms of pulverizers involve propelling the material with great force against a target.

Such apparatus and methods are not suitable where it is desired not to pulverize the material but to reduce it to substantially rounded particles of predetermined size. It has been found by the applicant that pulverization can be largely avoided and a rounded product obtained by propelling certain of the particles against other of the particles which are stationary with suflicient force to chip protruding corners including fracture of crystal structure of at least some of the moving and stationary particles. By fracturing the crystal structure of rock particles, a round product is obtained and by recycling over-size particles (hereinafter referred to as overs) most of the rock particles can be reduced substantially to a predetermined rounded size.

In one of its aspects, an impact mill for reducing the size of rock particles in accordance with this invention includes an elongated tube of predetermined length having a receiving end and a discharge end, an attrition bin disposed in co-operative alignment with said tube and communicating with the discharge end thereof, means for introducing rock particles to said tube, means for causing said particles to move through said tube at high velocity, whereby said particles are hurled from said discharge end into the attrition bin, said bin being adapted to accumulate said particles, said co-operative alignment of said bin with said tube serving to direct said particles hurled from the discharge end of said tube into collision with the particles accumulated in said bin to reduce the size of at least some of said particles.

In another of its aspects, an impact mill for reducing the size of rock particles includes at least two elongated tubes of predetermined length and an equal number of attrition bins, each of said tubes having a receiving end and a discharge end; said bins being co-operatively aligned in series with said tubes for the successive reduction of said particles; one of said discharge ends communicating with each of said bins; means for introducing rock particles to a selected first tube, means for impelling said particles through said selected first tube at high velocity into the bin communicating with the discharge end thereof, means for introducing rock particles in said bins to the receiving ends of said tubes, means for impelling said particles through said tubes at high velocity into the bins communicating with the discharge ends thereof, each of said bins being adapted to accumulate at least some of said particles, whereby said particles are impelled through said tubes from bin to bin and said co-operative alignment of said bins with said tubes serves to direct said particles impelled from the discharge ends of said tubes into collision with said accumulated particles in said bins to reduce the size of at least some of said particles.

In drawings which illustrate embodiments of the invention,

FIGURE 1 is a side elevation view of one embodiment,

FIGURE 2 is a diagrammatic plan view partly in section of another embodiment,

FIGURE 3 is a sectional elevation view taken along the lines 3-3 of FIGURE 2,

FIGURE 4 is a sectional elevation view taken along the lines 44 of FIGURE 2,

FIGURE 5 is an enlarged, detailed elevation view of the feed arrangement at point A in FIGURE 2,

FIGURE 6 is a sectional diagrammatic plan view of another embodiment,

FIGURE 7 is a sectional, diagrammatic elevation view of the embodiment of FIGURE 6, and

FIGURE 8 is a sectional view taken along the lines 8-8 of FIGURE 6.

The impact mill illustrated in FIGURE 1 comprises an elongated tube 10, having a receiving end 11 and a discharge end 12 communicating with an attrition bin 13. A fan 14 connected to the receiving end 11 of the tube is capable of creating winds of from 50 to 2.00 miles per hour in tube 10 to impel rock particles 15 through the tube and into the bins at high velocity. The rock particles 15 are introduced to the tube by the feed hopper 16 which is detachably connected to the tube 10 adjacent the receiving end 11 thereof. The feed hopper 16 includes a vibrating feeder 16' which introduces the particles 15 to the tube. An aperture 17 in root 18 of the bin 13 permits the escape of dust from the bin 13 and aperture 19 in the floor 20 of the bin is opened and closed by plate 21 slidably connected to the floor 20. From time to time the particles in the bin are withdrawn through aperture 19 and screened, with overs (not shown) being recycled. At the beginning of the reduction operation there will be particles in the bin so that those introduced to the tube 10 through the hopper 16 and impelled through the tube into the bin will collide with the stationary particles in the bin.

The impact mill illustrated in FIGURES 2 to 5 inclusive is a modification of that shown in FIGURE 1, in which four attrition bins 13 and four tubes 10 are cooperatively aligned in series for the successive reduction of rock particles. In the preferred arrangement, the bins will be erected on sloping ground (see FIGURE 4) with the first bin located highest on the slope, so that it will not be necessary to slope the tubes upwardly from bin to bin with consequent loss in momentum of the rock particles.

At the beginning of the reduction run each bin has a covering of particles 15 (not shown) to protect the bin floors 20. Each bin floor 2%) can be made of wood and comprises a sloping portion 23 and a substantially horizontal portion 24 adapted to hold a predetermined minimum quantity of rock particles in each bin to protect the floors thereof. The receiving end 11 of a selected first tube 22 communicates with the first bin. Rock particles (not shown) are introduced to the tube 22 by feed hopper 16 detachably connected thereto. The feed hopper 16 includes a vibrating feeder 16' which introduces the particles to the tube 22. Winds in tube 22 created by the fan 14 connected to the receiving end of the tube impel the rock particles in the tube at high velocity into the first bin. The rock particles impelled from the discharge end 12 of the tube 22 collide with the stationary rock particles in the bin. An aperture 25 in the horizontal portion 24,,of each bin fioor (see FIGURE 3). communicates with the next tube in the series, the receiving end of which is located beneath the bin floor. The particles over and above the predetermined minimum quan;

' tity in each bin necessary, to protect-the floor of the bins slides into the. aperture 25 and into the next tube when they are impelled at high velocity into the next bin in the series. In this way therock particlesprog-ressfrom the first selected tube, 22 to the first bin and from bin to bin via thetubes until ,the third or penultimate bin is' and screen may be placed at the bottom of theincline rather than at the'top so that the hopper and feeder only once handle anyrock. particle. With this system the airlock 26 may be located between the screens and the return duct so that the flow will be hopper'feeder--- screen-return. fan and duct-reduction bins-screen return fan and duct, etc. There would be no in'-circuit storage and no" i'n-circuit feeder. The rock particles would repeatedly passthrough the screen, air lock, returm fan andreduction bins inth at order.-: I I V An impact mill having a helical tube 33 is illustrated in FIGURES 6 to 8 inclusive. 1.1m" cross section (see FIGURE 8) the outer'wall 34 of the tube 33 i'sellipticah andthe inner Wall 35 is circular with the circular passage (not shown) is provided to convey the particles to the mill screen (also not shown). Air lock 26 is a louvc-red aperture (details not shown) and the louvers areadapted to close in the event lOf back pressure it the productreturn duct 27, thereby preventing blow backs in that duct.v The duct 27 leads to a mill screen (not shown) where the particles are sized. Overs are recycled,

As the rock particles, hurled into the bins from the.

discharge ends of the tubes, come into collision with the stationary particles in the, bins, considerable dust is' created. Advantage is taken of the air stream issuing from the discharge ends \of the tubes into the attrition bins to remove this .dust. A directional blafile 30 is l-ocatedin each bin being disposed parallelto the bin floor 20 in spaced relationship from the front wall 31 of each. bin. As the prpductladen air stream enters an at trition bin the air flow is as shown by the broken line in FIGURE 3. The air bounded by the baffle 30 and the near 20 will be in turbulence and the heavier rock parti oles' will either roll down'the bin floor 20 or fall out ot the air stream as it passes along the underside of the.

baflle 30.; These particles will find their way to the apenture" 25in the bin floor and through which they will pass and then be carried to the next bin by the. next tube.-

The dust will be comparatively lighter than the product and since the air in the bins will be underpressure from the, air issuing from the discharge ends of the tubes, the dust will be carried by the air stream into the areabetween the tworows of attrition bins, in which area when the stream issues from one of the bins it merges smoothly with the downward flow of dust laden air.

While drawings 2 to 5 inclusive illustrate a seriesof fiour bins and four tubes being a modification :of the embodiment shown in FIGURE 1, it is not intended to, infer that four is the maximum or optimum number of bins. It. may be that as many as forty or more bins will, prove desirable. The decision will be based upon such variables as the size of the rock particles to bereduced, the contour of the ground on which the bins are'to be erected, the degree of roundness of the produce required, the inacture habit of the particular rock used for raw material and the velocity of the collision between'the moving and the stationary rock particles. The velocity itself will vary with air-speed, air-turbulence, mill dimensions and dryness of feed and air humidity. The fracture habit of the A second directionalbaffie 32 in each 1 36 being radially inwardly oIt-setrfrom the central axisof, the tubeso that the greatest thickness of hte tube walli is at the .outerperinieter of the helix." Crushed rock parti-- cles" from ac'rushing plant (not shown) are stored in'the' mill bin 37 from which the r'ockparticle'sv are conveyed by a belt conveyor 38 to thevibrating screen 39 where the rock' particles are separated into three sizes, namely, fines, overs, and :produc The fines will be stored: and run through the tube at a later date for a secondary product. 'The overs will drop down into the air strearnof the helical mill created'by'the fan 40 located: in the receiving end of the" helical inseam as the particles are blown through'the. helical tube they tend to roll? around the wall of the-Ltube' becoming rounded in the:

process. Atthe discharge endv of the, helical tube, the" rock particles are impelled into the attrition bin 41 which functions similarly to those previouslydescribed and where further reduction in size occurs when the discharged particles collide with stationary particles in the bin. From the attrition bin the rock particles'again pass over the'screen and are furtherseparated asin the first instance. The overs-wil1again be put through the tube-'- and the .fines will be conveyed to storage. The" prod uc will be placed in storage bins (not shown) ready" for shipment. When secondary products are to be run the. vibratingwscreens will be changed to the required meshes.

In-its preferred embodiment, the helical tube is molded of concrete. 7 v a All three embodiments of the invention have the same purpose, which is to change the geometrical shape 6t the rock particles from angular to spherical.

Throughout thedescription of .the illustrated embodiments of the invention the means fior impclling the rock particles through the tubes has been a fan creating winds 7 of air of substantial force in the tubes. It is notnecessary that the conveying medium be air. Other gases will work.

When'c0llision occurs between impelled particlesof 7 rock and stationary particles of rocks as hereinbefcre rock is dependent on tectonics ofthe habitat of the rock,

the crystal size and composition and the degree of 'inter- I the particles.

described the impact is of a very high order compared with the impact between nearly parallel moving suspended particles, and such impact results in the fracture of the. crystal structure of the rock particles. In effect it is a selective reduction of the more protruding parts of the:

grains of the rock particles with a consequent rounding of the particles being reduced in size. Applicant employs the invention to make a coarse sand and any powder size material obtained is a by product. i

Depending on the nature of the rock particles being;

used, it may prove feasible, to increase the wind range,

of the fans upto 500 miles per hour without pulverizing; v However, applicant con-templates using. rock particles largely composed of quartz and has found. that winds in excess of 200 miles per hour have caused. the particles topulverize' each other ratherthan. to free? ture the grain structure of the. pafiticles- It is only necessary that the conveying medium has aviscosity sufliciently low that it will not lubricate I claim:

1. An impact mill for reducing the size of rock particles including an elongated tube of predetermined length having a receiving end and a discharge end, an attrition bin disposed in co-operative alignment with said tube and communicating with the discharge end thereof, means for introducing rock particles to said tube, means for impelling said particles through said tube at high velocity, whereby said particles are hurled from said discharge end into the attrition bin, said bin being adapted to accumulate at least some of said particles, said co-operative alignment of said bin with said tube serving to direct said particles hurled from the discharge end of said tube into collision with the particles accumulated in said bin to reduce the size of at least some of said particles.

2. An impact mill according to claim 1 in which the means for introducing rock particles to said tube includes a feed hopper detachably connected to the tube adjacent the receiving end thereof.

3. An impact mill according to claim 2 including an aperture for removing dust from said bin and a closable aperture in the floor of said bin through which rock particles can be withdrawn.

4. An impact mill according to claim 3 in which the means for impelling the particles at high velocity through the tube comprises a fan in the receiving end of said tube capable of creating high velocity winds in said tube in the range from to 50 to 500 miles per hour, said Winds serving to force said particles to move at high velocity along said tube.

5. An impact mill according to claim 1 in which the tube is helical and the discharge end thereof is elevated relative to the receiving end thereof.

6. An impact mill according to claim 1 in which the tube is made of concrete.

7. An impact mill for reducing the size of rock particles, said mill including at least two elongated tubes of predetermined length and an equal number of attrition bins, each of said tubes having a receiving end and a discharge end; said bins being co-operatively aligned in series with said tubes for the successive reduction of said particles; one of said discharge ends communicating with each of said bins; means for introducing rock particles to a selected first tube, means for impelling said particles through said selected first tube at high velocity into the bin communicating with the discharge end thereof, means for introducing rock particles in said bins to the receiving ends of said tubes, means for impelling said particles through said tubes at high velocity into the bins communicating with the discharge ends thereof, each of said bins being adapted to accumulate at least some of said particles, whereby said particles are impelled through said tubes from bin to bin and said co-operative alignment of said bins with said tubes serves to direct said particles impelled from the discharge ends of said tubes into collision with said accumulated particles in said bins to reduce the size of at least some of said particles.

8. An impact mill according to claim 7 in which the means for introducing rock particles in each successive bin to the receiving ends of said tubes comprises an aperture in the floor of each of said bins, each of said apertures communicating with the receiving end of the tube having its discharge end communicating with the next bin in said series.

9. An impact mill according to claim 8 including a louvered aperture toward the receiving end of the tube having its discharge end communicating with the last bin in said series, said louvers being adapted to close said aperture when back pressure arises.

References Cited by the Examiner UNITED STATES PATENTS 245,584 8/81 Toulmin 241-39 X 1,753,437 4/30 Lykken 241-284 X 1,791,100 2/31 Lykken 241-39 X 2,939,189 6/60 Wenninger 241-40 X I. SPENCER OVERHOLSER, Primary Examiner.

ROBERT A. OLEARY, Examiner. 

1. AN IMPACT MILL FOR REDUCING THE SIZE OF ROCK PARTICLES INCLUDING AN ELONGATED TUNE OF PREDETERMINED LENGTH HAVING A RECEIVING END AND A DISCHARGE END, AN ATTRITION BIN DISPOSED IN CO-OPERATIVE ALIGNMENT WITH SAID TUBE AND COMMUNICATING WITH THE DISCHARGE END THEREOF, MEANS FOR INTRODUCING ROCK PARTICLES TO SID TUBE, MEANS FOR IMPELLING SAID PARTICLES THROUGH SAID TUBE AT HIGH VELOCITY WHEREBY SAID PARTICLES ARE HURLED FROM SAID DISCHARGE END INTO THE ATTRITION BIN, SAID BIN BEING ADAPTED TO ACCUMULATE AT LEASE SOME OF SAID PARTICLES, SAID CO-OPERATIVE ALIGNMENT OF SAID BIN WITH SAID TUBE SERVING TO DIRECT SAID PARTICLES HURLED FROM THE DISCHARGE END OF SAID TUBE INTO COLLISION WITH THE PARTICLES ACCUMULATED IN SAID BIN TO REDUCE THE SIZE OF AT LEAST SOME OF SAID PARTICLES. 